Method of etching silicon-containing film, computer-readable storage medium, and apparatus for etching silicon-containing film

ABSTRACT

There is provided a method of etching a silicon-containing film formed on a substrate, the method including: etching the silicon-containing film by using both a first fluorine-containing gas and a second fluorine-containing gas, the first fluorine-containing gas including at least an F2 gas and the second fluorine-containing gas including at least a ClF3 gas, an IF7 gas, an IF5 gas or an SF6 gas.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2018-094597, filed on May 16, 2018, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a method of etching asilicon-containing film formed on a substrate, a computer-readablerecording medium, and an apparatus for etching the silicon-containingfilm.

BACKGROUND

In the field of semiconductor device, a silicon-containing film isapplied to a wide variety of applications. For example, a silicon (Si)film is used for a gate electrode, a seed layer and the like. In aprocess of manufacturing semiconductor devices, the Si film formed on asubstrate is etched.

Various techniques have been used to etch a silicon-containing film suchas a Si film or the like. For example, there is known a technique thatetches a Si layer with a halogen fluoride gas such as ClF₃. In addition,there is known a technique that etches Si with an etching gas systemincluding an F₂ gas and an NH₃ gas.

It is sometimes required that a surface roughness of asilicon-containing film after etching is small. However, the aboveconventional etching techniques do not take into consideration thesurface roughness.

Further, there is a case where a pattern is formed on a substrate by anoxide film or the like before etching a silicon-containing film formedon a substrate and a hole is formed in the pattern to expose an etchingtarget portion of the silicon-containing film. In this case, there is aneed of planarizing a front surface of the etched silicon-containingfilm in the hole. However, the conventional etching techniques do nottake into consideration the planarization of the silicon-containing filmin the hole of the pattern.

Therefore, there is room for improvement in the conventionalsilicon-containing film etching technique.

SUMMARY

Some embodiments of the present disclosure provide a technique capableof reducing a surface roughness of a silicon-containing film whenetching the silicon-containing film formed on a substrate, and atechnique capable of planarizing a surface of a silicon-containing filmwhen etching the silicon-containing film formed on a substrate having apattern in which a hole is formed so as to expose an etching targetportion in the hole.

According to one embodiment of the present disclosure, there is provideda method of etching a silicon-containing film formed on a substrate, themethod including: etching the silicon-containing film by using both afirst fluorine-containing gas and a second fluorine-containing gas, thefirst fluorine-containing gas including at least an F₂ gas and thesecond fluorine-containing gas including at least a ClF₃ gas, an IF₇gas, an IF₅ gas or an SF₆ gas.

According to another embodiment of the present disclosure, there isprovided a non-transitory computer-readable storage medium storing aprogram that operates on a computer of a controller for controlling anetching apparatus and that causes the computer to perform theaforementioned etching method by the etching apparatus.

According to another embodiment of the present disclosure, there isprovided an apparatus for etching a silicon-containing film formed on asubstrate, including: a chamber in which the substrate is accommodated;and a gas supply part configured to supply both a firstfluorine-containing gas and a second fluorine-containing gas onto thesilicon-containing film, the first fluorine-containing gas including atleast an F₂ gas, and the second fluorine-containing gas including atleast a ClF₃ gas, an IF₇ gas, an IF₅ gas or an SF₆ gas.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the presentdisclosure, and together with the general description given above andthe detailed description of the embodiments given below, serve toexplain the principles of the present disclosure.

FIG. 1 is a schematic sectional view of a silicon-containing film to beetched by an etching apparatus according to an embodiment.

FIG. 2 is a longitudinal sectional view schematically showing theconfiguration of the etching apparatus according to the embodiment.

FIG. 3 is an SEM image showing a surface state of a polysilicon filmwhen a polysilicon blanket is etched using a set of F₂ gas and NH₃ gas.

FIG. 4 is an SEM image showing a surface state of a polysilicon filmwhen a polysilicon blanket is etched using a ClF₃ gas alone.

FIG. 5 is an SEM image showing a surface state of a polysilicon filmwhen a polysilicon blanket is etched using both the set of F₂ gas andNH₃ gas and the ClF₃ gas.

FIGS. 6A and 6B are explanatory views showing an etching state availablewhen the set of F₂ gas and NH₃ gas are used as etching gases.

FIGS. 7A and 7B are explanatory views showing an etching state when onlythe ClF₃ gas is used as an etching gas.

FIG. 8 is a schematic sectional view showing the shape of the surface ofa Si film when a patterned Si film is etched using the set of F₂ gas andNH₃ gas.

FIG. 9 is a schematic sectional view showing the shape of the surface ofa Si film when a patterned Si film is etched using the ClF₃ gas alone.

FIG. 10 is a schematic sectional view showing the shape of the surfaceof a Si film when a patterned Si film is etched using both the set of F₂gas and NH₃ gas and the ClF₃ gas.

FIGS. 11A to 11E are explanatory views showing an etching state of a Sifilm in a hole of a pattern when the ClF₃ gas and the set of F₂ gas andNH₃ gas are used as etching gases.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings. In the subject specification and thedrawings, components having substantially identical functions andconfigurations will be designated by like reference numerals with theduplicate descriptions thereof omitted. In the following detaileddescription, numerous specific details are set forth in order to providea thorough understanding of the present disclosure. However, it will beapparent to one of ordinary skill in the art that the present disclosuremay be practiced without these specific details. In other instances,well-known methods, procedures, systems, and components have not beendescribed in detail so as not to unnecessarily obscure aspects of thevarious embodiments.

As a result of the earnest research conducted by the present inventors,it was found that, by etching a silicon-containing film with both afirst fluorine-containing gas and a second fluorine-containing gas ontothe silicon-containing film, the first fluorine-containing gas beinginclusive of at least an F₂ gas, and the second fluorine-containing gasbeing inclusive of at least a ClF₃ gas, an IF₇ gas, an IF₅ gas or an SF₆gas, it is possible to reduce a surface roughness of the etchedsilicon-containing film. In addition, as a result of the earnestresearch conducted by the present inventors, it was found that, byetching a silicon-containing film formed in a hole with both the firstfluorine-containing gas and the second fluorine-containing gas, it ispossible to planarize a surface of the etched silicon-containing film inthe hole. A method of reducing the surface roughness of the etchedsilicon-containing film and planarizing the surface of the etchedsilicon-containing film in the hole by using both the firstfluorine-containing gas and the second fluorine-containing gas, will bedescribed in detail in the following embodiments.

<Etching Apparatus>

First, the configuration of an etching apparatus according to anembodiment of the present disclosure and a silicon-containing film to beetched by the etching apparatus will be described. FIG. 1 is a schematicview of a silicon-containing film to be etched by an etching apparatus 1according to an embodiment. FIG. 2 is a longitudinal sectional viewschematically showing the configuration of the etching apparatus 1according to the embodiment.

In this embodiment, as shown in FIG. 1, a silicon-containing film S tobe etched is formed on a wafer W as a substrate. The wafer W has apattern P constituted by an oxide film or the like in which a hole Pa isformed. The silicon-containing film S formed inside the hole Pa andexposed from a front surface of the wafer W through the hole Pa is anetching target. In this embodiment, the silicon-containing film S as theetching target is a Si film (hereinafter sometimes referred to as a Sifilm S). The oxide film constituting the pattern P is, for example, anSiO₂ film.

As shown in FIG. 2, the etching apparatus 1 includes a chamber 10 inwhich the wafer W is accommodated, a mounting table 11 provided insidethe chamber 10 to mount the wafer W thereon, an gas supply part 12 forsupplying a process gas from above the mounting table 11 toward themounting table 11, and an exhaust part 13 for discharging the processgas from the interior of the chamber 10. Etching performed in theetching apparatus 1 is a plasma-less gas etching.

The chamber 10 includes a chamber body 20 and a lid 21. An upper portionof the chamber body 20 is opened to define an opening. The opening isclosed by the lid 21. An upper surface of the side wall of the chamberbody 20 and a lower surface of the lid 21 are hermetically sealed by aseal material (not shown) to secure airtightness in the chamber 10.Thus, an airtight etching processing space is formed inside the chamber10. A loading/unloading port (not shown) through which the wafer W istransferred is formed in the side wall of the chamber body 20. Theloading/unloading port can be opened and closed by a gate valve (notshown).

The mounting table 11 includes an upper table 30 on which the wafer W ismounted, and a lower table 31 that is fixed to a bottom surface of thechamber body 20 and supports the upper table 30. A temperature adjustingpart 32 for adjusting a temperature of the wafer W is provided insidethe upper table 30. The temperature adjusting part 32 adjusts atemperature of the mounting table 11 by circulating a temperatureadjustment medium such as water such that the temperature of the wafer Wmounted on the mounting table 11 is controlled to a predeterminedtemperature.

The gas supply part 12 includes a shower head 40 for supplying theprocess gas onto the wafer W mounted on the mounting table 11. Theshower head 40 is provided on a lower surface of the lid 21 of thechamber 10 so as to face the mounting table 11. A plurality of supplyports 41 through which the process gas is supplied is formed in a lowersurface (shower plate) of the shower head 40. The shower head 40 mayhave a diameter larger than at least that of the wafer W in order tosupply the process gas uniformly onto the entire surface of the wafer Wmounted on the mounting table 11.

The gas supply part 12 further includes an F₂ gas supply source 50 forsupplying an F₂ gas, an NH₃ gas supply source 51 for supplying an NH₃gas, a ClF₃ gas supply source 52 for supplying a ClF₃ gas, and a N₂ gassupply source 53 for supplying an N₂ gas. An F₂ gas supply pipe 54 isconnected to the F₂ gas supply source 50, an NH₃ gas supply pipe 55 isconnected to the NH₃ gas supply source 51, a ClF₃ gas supply pipe 56 isconnected to the ClF₃ gas supply source 52, and an N₂ gas supply pipe 57is connected to the N₂ gas supply source 53. The supply pipes 54 to 57are connected to a collective pipe 58 that is connected to the showerhead 40. The F₂ gas, the NH₃ gas, the ClF₃ gas and the N₂ gas aresupplied from the shower head 40 into the chamber 10 via the respectivesupply pipes 54 to 57 and the collective pipe 58.

Flow rate adjusters 59 configured to control opening/closing operationsof the respective supply pipes 54 to 57 and flow rates of the respectiveprocess gases are respectively provided in the F₂ gas supply pipe 54,the NH₃ gas supply pipe 55, the ClF₃ gas supply pipe 56 and the N₂ gassupply pipe 57. Each of the flow rate adjusters 59 is constituted by,for example, an ON-OFF valve and a mass flow controller.

The process gas supplied from the gas supply part 12 includes twodifferent fluorine-containing gases for etching the silicon-containingfilm. One of the two different fluorine-containing gases is defined as afirst fluorine-containing gas including the F₂ gas and the NH₃ gas, andthe other is defined as a second fluorine-containing gas including theClF₃ gas. A gas mixed with the F₂ gas is not limited to the NH₃ gas butmay be any basic gas. The N₂ gas is used as a dilution gas or a purgegas. Instead of the N₂ gas, other inert gas such as an Ar gas may beused, or two or more kinds of inert gases may be used.

In the gas supply part 12 of this embodiment, the process gas issupplied from the shower head 40 to the wafer W. However, the method ofsupplying the process gas is not limited thereto. For example, a gassupply nozzle (not shown) may be provided in the central portion of thelid 21 of the chamber 10, and the process gas may be supplied from thegas supply nozzle.

The exhaust part 13 includes an exhaust pipe 60 provided at the bottomof the chamber body 20 of the chamber 10 outward of the mounting table11. An exhaust mechanism 61 configured to evacuate the interior of thechamber 10 is connected to the exhaust pipe 60. An automatic pressurecontrol valve (APC) 62 is provided in the exhaust pipe 60. An internalpressure of the chamber 10 is controlled by the exhaust mechanism 61 andthe automatic pressure control valve 62.

The etching apparatus 1 is provided with a control part 70. The controlpart 70 is, for example, a computer, and includes a program storage (notshown). A program for controlling the etching process performed in theetching apparatus 1 is stored in the program storage. The program may berecorded in a non-transitory computer-readable storage medium such as acomputer-readable hard disk (HD), a flexible disk (FD), a magnetooptical disk (MO), memory card or the like, and may be installed fromthe storage medium on the control part 70.

<Etching Method>

Next, an etching method in the etching apparatus 1 configured as abovewill be described. As described above, the etching apparatus 1 of thisembodiment etches the Si film formed on the wafer W.

First, with the gate valve opened, the wafer W is loaded into thechamber 10 and mounted on the mounting table 11. The temperature of themounting table 11 has been adjusted by the temperature adjusting part 32so that the temperature of the wafer W mounted on the mounting table 11is controlled to a predetermined temperature. In addition, once thewafer W is mounted on the mounting table 11, the gate valve is closed tomake the interior of the chamber 10 airtight. Thus, an etchingprocessing space is formed inside the chamber 10.

Thereafter, the interior of the chamber 10 is evacuated. While adjustingthe internal pressure of the chamber 10, the ClF₃ gas as an etching gasis supplied into the chamber 10 to each Si film formed on the wafer W.At this time, in addition to the ClF₃ gas, a N₂ gas may be supplied as adilution gas.

Subsequently, the N₂ gas as a purge gas is supplied into the chamber 10to purge the interior of the chamber 10 while evacuating the interior ofthe chamber 10 again.

Thereafter, while adjusting the internal pressure of the chamber 10, theF₂ gas and the NH₃ gas are supplied as etching gases into the chamber 10to further etch the Si film formed on the wafer W. At this time, the N₂gas may be added as a dilution gas.

Subsequently, the N₂ gas as a purge gas is supplied into the chamber 10to purge the interior of the chamber 10 while evacuating the interior ofthe chamber 10 again.

Thereafter, the above-described steps are repeated so that the ClF₃gas-based etching and the F₂ gas/NH₃ gas-based etching are performedalternately a predetermined number of times.

While in the above embodiment, the ClF₃ gas-based etching is initiallyperformed, the F₂ gas/NH₃ gas-based etching may be initially performed.In addition, while in the above example, the number of times of the ClF₃gas-based etching and the number of times of the F₂ gas/NH₃ gas-basedetching have been described to be equal to each other, they may bedifferent from each other. In some embodiments, two types of etchingsincluding the ClF₃ gas-based etching and the F₂ gas/NH₃ gas-basedetching may be alternately performed a predetermined number of times andsubsequently, the first etching of the two types of etchings may beagain performed last.

<Effects of the Present Embodiment>

Next, the effects of the present embodiment will be described.

Verification was conducted under various etching conditions by thepresent inventors. As a result, the present inventors have found that,by using both the first fluorine-containing gas including the F₂ gas andthe NH₃ gas and the second fluorine-containing gas including the ClF₃gas as the etching gases in etching the Si film, the surface roughnessof the silicon-containing film after etching can be reduced. The abovefindings will be described below.

In the related art, either one of the F₂ gas/the NH₃ gas and the ClF₃gas was used as an etching gas for the Si film. In this regard, thepresent inventors conducted comparison/verification with respect to thesurface roughness of an etched silicon-containing film in the case ofusing the set of F₂ gas and NH₃ gas, and the case of using the ClF₃ gasalone. As a result of the comparison, it was found that the state of thesurface of the etched silicon-containing film showed the oppositetendency in the case of using both the set of F₂ gas and NH₃ gas and thecase of using the ClF₃ gas alone.

The results of the verification are shown in FIGS. 3 and 4. FIG. 3 is ascanning electron microscope (SEM) image showing the surface state of apolysilicon film when a polysilicon blanket is etched using the set ofF₂ gas and NH₃ gas. FIG. 4 is an SEM image showing the surface state ofa polysilicon film when a polysilicon blanket is etched using the ClF₃gas alone. An arithmetic average roughness Sa of the polysilicon filmbefore etching was 2.5 nm, and a root-mean-square roughness RMS was 3.1nm.

As shown in FIG. 3, when the etching was performed using the set of F₂gas and NH₃ gas, irregularities having a large aspect ratio and a narrowinterval between adjacent irregularities were formed on a surface of apolysilicon film Sp after the etching. When polysilicon was etched usingthe set of F₂ gas and NH₃ gas, the arithmetic average roughness Sa was6.7 nm and the root-mean-square roughness RMS was 8.3 nm.

On the other hand, as shown in FIG. 4, when the etching is performedusing the ClF₃ gas alone, irregularities having a small aspect ratio anda wide interval between adjacent irregularities were formed on thesurface of the polysilicon film Sp after the etching. When polysiliconwas etched using the ClF₃ gas alone, the arithmetic average roughness Sawas 3.40 nm and the root-mean-square roughness RMS was 4.38 nm.

As described above, the state of the surface of the etched polysiliconfilm, namely the silicon-containing film, showed the opposite tendencyin the case of using both the set of F₂ gas and NH₃ gas and the case ofusing the ClF₃ gas alone.

The results shown in FIGS. 3 and 4 were obtained for the case where thesilicon-containing film to be etched is a polysilicon blanket. Similarresults were obtained for the case where the Si film S formed in thehole Pa of the pattern on the wafer W as shown in FIG. 1 was etched.

Based on these results, the present inventors conducted etching usingboth the set of F₂ gas and NH₃ gas and the ClF₃ gas. FIG. 5 is an SEMimage showing the surface state of polysilicon when a polysiliconblanket is etched using both the set of F₂ gas and NH₃ gas and the ClF₃gas. The verification result of FIG. 5 was obtained by alternatelyperforming the etching based on the ClF₃ gas and the etching based onthe set of F₂ and NH₃ gas twice, and subsequently, performing theetching based on the ClF₃ gas again.

As shown in FIG. 5, the surface roughness of the etched polysiliconfilm, which is available when using both the set of F₂ gas and NH₃ gasand the ClF₃ gas, can be smaller than that available when using any oneof the set of F₂ gas and NH₃ gas and the ClF₃ gas. When etchingpolysilicon with both the set of F₂ gas and NH₃ gas and the ClF₃ gas,the arithmetic average roughness Sa was 2.0 nm and the root-mean-squareroughness RMS was 2.5 nm. Similar results were obtained for the casewhere the silicon-containing film to be etched was the Si film S formedin the hole Pa of the pattern on the wafer W as shown in FIG. 1.

As described above, according to the verification results shown in FIGS.3 to 5, by using both the set of F₂ gas and NH₃ gas and the ClF₃ gas, itis possible to reduce the surface roughness of the etched Si film.

<Mechanism of Surface Roughness Improvement>

Next, the mechanism by which the surface roughness of the etched Si filmcan be reduced by using both the set of F₂ gas and NH₃ gas and the ClF₃gas as described above will be described. FIGS. 6A and 6B areexplanatory views showing the state of a Si film when being etched withthe set of F₂ gas and NH₃ gas. FIGS. 7A and 7B are explanatory viewsshowing the state of a Si film when being etched with the ClF₃ gasalone. FIGS. 6A and 7A show the state of the Si film before the etching,and FIGS. 6B and 7B show the state of the Si film after the etching.

It is assumed that the silicon-containing film to be etched is apolysilicon film. The Si film S as a polysilicon film has grains Ghaving different crystal orientations, and a crystal grain boundary Bexists between the grains G.

Etching progresses through diffusion/supply and adsorption of reactivespecies onto the surface, formation of reaction products, anddesorption/diffusion of the reaction products from the surface. The F₂gas has weak reactivity. Thus, it is considered that the etchingprogresses for not only the grain boundaries B but also the entiregrains G, thereby forming irregularities having relatively narrowintervals.

On the other hand, the ClF₃ gas has a much stronger reactivity than thatof the F₂ gas. Thus, in the case of using the ClF₃ gas alone, theetching progresses for the entire Si film S, and particularly tends toconcentratively progress for the crystal grain boundaries B having weakcoupling. As a result, it is considered that irregularities having wideintervals are formed. Thus, the progression of the etching based on theClF₃ gas alone may further facilitate the formation of theirregularities.

Utilizing these features, it is conceived that, by combining a method offinely etching the Si film to be etched and a method of widely etchingthe Si film to be etched at a high speed with both the F₂ gas and theClF₃ gas, it is possible to make the surface of the etched Si film flat.

In a case where the silicon-containing film to be etched is an amorphoussilicon film, the amorphous silicon film has a lump-like structure likethe polysilicon film and thin grains present between the lumps. Thus, itis thought that the etching progresses for the amorphous silicon filmwith both the F₂ gas and the ClF₃ gas, like the polysilicon film.

<Other Effects of the Present Embodiment>

Next, other effects of the present embodiment will be described.

Verification was conducted under various etching conditions by thepresent inventors. As a result, the present inventors have found that,by etching a Si film on a substrate having a pattern in which a hole isformed so as to expose an etching target portion, using both the firstfluorine-containing gas including the F₂ gas and the NH₃ gas and thesecond fluorine-containing gas including the ClF₃ gas as the etchinggases, the surface of the etched Si film in the hole can be flattened.Such findings will be described below.

As described above, in the related art, one of the set of F₂ gas and NH₃gas and the ClF₃ gas was used as an etching gas for the Si film. In thisregard, the present inventors conducted comparison/verification withrespect to the flatness of the surface of the etched Si film in the holeof the pattern in the case of using the set of F₂ gas and NH₃ gas andthe case of using the ClF₃ gas alone. As a result of the comparison, itwas found that the shape of the surface of the etched Si film showed theopposite tendency in the case of using the set of F₂ gas and NH₃ gas andthe case of using the ClF₃ gas alone.

The results of the verification are shown in FIGS. 8 and 9. FIG. 8 is aschematic sectional view showing the shape of the surface of a Si filmwhen a patterned Si film is etched with the set of F₂ gas and NH₃ gas.FIG. 9 is a schematic sectional view showing the shape of the surface ofthe Si film when the patterned Si film is etched with the ClF₃ gasalone.

As shown in FIG. 8, when the etching was performed using the F₂ gas andthe NH₃ gas, the surface of the etched Si film S in the hole Pa of thepattern P had an upwardly-protruded convex shape. On the other hand, asshown in FIG. 9, when the etching was performed using the ClF₃ gas, thesurface of the etched Si film in the hole Pa of the pattern P had adownwardly-recessed concave shape.

As described above, the shape of the surface of the etched Si film inthe hole Pa of the pattern P showed the opposite tendency in the case ofusing the set of F₂ gas and NH₃ gas and the case of using the ClF₃ gasalone. In other words, in the case of using the set of F₂ gas and NH₃gas and the case of using the ClF₃ gas alone, different etching ratesare manifested at the central portion and the peripheral portion of thehole Pa.

Based on these results, the present inventors conducted etching with theset of F₂ gas and NH₃ gas and the ClF₃ gas. FIG. 10 is a schematicsectional view showing the shape of the surface of the Si film when thepatterned Si film is etched using the set of F₂ gas and NH₃ gas and theClF₃ gas. The verification results of FIG. 10 were obtained by initiallyperforming the supply of the set of F₂ gas and NH₃ gas and subsequently,alternately performing the supply of the set of F₂ gas and NH₃ gas andthe supply of the ClF₃ gas alone twice.

As shown in FIG. 10, by using both the set of F₂ gas and NH₃ gas and theClF₃ gas, the surface of the etched Si film S in the hole Pa of thepattern P becomes flat.

As described above, according to the verification results shown in FIGS.8 to 10, by using both the set of F₂ gas and NH₃ gas and the ClF₃ gas,it is possible to planarize the surface of the etched Si film in thehole of the pattern formed on the wafer W.

<Planarization Mechanism>

Next, the mechanism by which the surface of the etched Si film in thehole of the pattern can be planarized using both the set of F₂ gas andNH₃ gas and the ClF₃ gas as described above will be described. FIGS. 11Ato 11E are explanatory views showing the state of the surface of the Sifilm in the hole of the pattern when the etching is performed using theClF₃ gas and the F₂ gas and the NH₃ gas.

Prior to describing the planarization mechanism, a mechanism in whichthe surface of the Si film in the hole becomes concave when using theClF₃ gas alone and a mechanism in which the surface of the Si film inthe hole becomes convex when using the set of F₂ gas and NH₃ gas, willbe described.

The ClF₃ gas and the set of the F₂ gas and the NH₃ gas differ from eachother not only in their molecular weights but also in the surfaceadsorption onto the Si film and the characteristics of reaction with theSi film. In addition, as the etching of the Si film S progresses, thedensity of etching gas molecules reaching the surface of the Si film Sbecomes higher in the central portion rather than in the peripheralportion in the hole Pa of the pattern P. In the case of using the ClF₃gas alone, due to the adsorption of the ClF₃ gas onto the surface of theSi film or the reactivity of the ClF₃ gas, it is difficult for the ClF₃gas to be diffused in a direction parallel to the surface of the wafer Walong the surface or the like of the Si film S in the hole Pa of thepattern P. Therefore, in the case of using the ClF₃ gas alone as theetching gas for the Si film S, it is thought that the surface of theetched Si film in the hole Pa of the pattern P has a downwardly-recessedconcave shape as shown in FIG. 9.

On the other hand, in the case of using only the F₂ gas and the NH₃ gas,the F₂ gas and the NH₃ gas is likely to be diffused in the hole Pa ofthe pattern P due to the adsorption of the F₂ gas and the NH₃ gas on thesurface of the Si film S or the reactivity thereof. Therefore, theetching of the Si film S is hardly performed at the central portion ofthe hole Pa as compared with the case of using the ClF₃ gas alone. Inaddition, the etching is performed over a plurality of divided cycles.Many reaction products generated in a preceding cycle due to thepresence of the NH₃ gas remain in the peripheral portion in the hole Paduring exhaust between the cycles. The etching using only the F₂ gas andthe NH₃ gas is promoted by such reaction products. As a result, theetching progresses more in the peripheral portion than in the centralportion in the hole Pa. Therefore, in the case of etching the Si film Swith only the set of F₂ gas and NH₃ gas as the etching gas, it isthought that the surface of the etched Si film in the hole Pa of thepattern P has an upwardly-protruded convex shape as shown in FIG. 8.

It is assumed that both the ClF₃ gas and the set of F₂ gas and NH₃ gasare used. For example, when the set of F₂ gas and NH₃ gas is initiallyused, as shown in FIG. 11A, the above-mentioned reaction products Hpresent evenly in the hole Pa. Thus, the surface of the etched Si film Sin the hole Pa is substantially flat. However, the etching amount isinsufficient at this stage. Thereafter, when exhaust is performed, asshown in FIG. 11B, the reaction products H present while being biased tothe peripheral portion in the hole Pa. Subsequently, when the etching isperformed with the ClF₃ gas, as described above, due to the adsorptionof the ClF₃ gas onto the surface or the reactivity of the ClF₃ gas, thesurface of the etched Si film in the hole Pa of the pattern P has aconcave shape as shown in FIG. 11C. Thereafter, exhaust is performed andthe set of F₂ gas and NH₃ gas is used. The etching of the Si film in thehole Pa is promoted in the peripheral portion rather than in the centralportion by the reaction products H. As a result, the surface of theetched Si film in the hole Pa has a convex shape as shown in FIG. 11D.Thereafter, exhaust is performed and the ClF₃ gas is used. Thus, thehole Pa is likely to be etched in the central portion whose filmthickness is relatively thick. As a result, the surface of the etched Sifilm in the hole Pa has a flat shape as shown in FIG. 11E. Accordingly,the planarization mechanism is effective.

<Other Embodiments>

While in the above embodiments, the Si film etching method has beendescribed, the method of the present disclosure may also be applied toother silicon-containing films.

For example, when etching a silicon germanium (SiGe) film, both a firstfluorine-containing gas exclusive of the NH₃ gas but inclusive of the F₂gas and a second fluorine-containing gas inclusive of the ClF₃ gas areused as etching gases.

In the above example, the second fluorine-containing gas different fromthe first fluorine-containing gas inclusive of the F₂ gas includes theClF₃ gas, but not limited thereto. The second fluorine-containing gasmay include at least a ClF₃ gas, an IF₇ gas, an IF gas or an SF₆ gas.

In the above embodiments, the first fluorine-containing gas inclusive ofthe F₂ gas and the second fluorine-containing gas inclusive of the ClF₃gas has been described to be alternately supplied, but not limitedthereto. The first fluorine-containing gas and the secondfluorine-containing gas may be mixed and supplied simultaneously asetching gases.

In some embodiments, assuming that one step including the etching usingthe first fluorine-containing gas, the exhaust of the firstfluorine-containing gas, the etching using the secondfluorine-containing gas, and the exhaust of the secondfluorine-containing gas is repeated, the amount of etching in each stepmay be gradually reduced. This makes it possible to further reduce thesurface roughness of the etched silicon-containing film.

According to the present disclosure in some embodiments, when etching asilicon-containing film formed on a substrate, it is possible to reducea surface roughness of the etched silicon-containing film. Further, whenetching a silicon-containing film formed on a substrate having a patternin which a hole is formed so as to expose an etching target portion, itis possible to planarize the surface of the etched silicon-containingfilm in the hole.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosures. Indeed, the embodiments described herein maybe embodied in a variety of other forms. Furthermore, various omissions,substitutions and changes in the form of the embodiments describedherein may be made without departing from the spirit of the disclosures.The accompanying claims and their equivalents are intended to cover suchforms or modifications as would fall within the scope and spirit of thedisclosures.

What is claimed is:
 1. A method of etching a silicon-containing filmformed on a substrate, the method comprising: etching, without using aplasma, the silicon-containing film in an etching apparatus by supplyinga first fluorine-containing gas and a second fluorine-containing gas byturns, the first fluorine-containing gas including at least an F₂ gasand the second fluorine-containing gas including at least a ClF₃ gas, anIF₇ gas, an IF₅ gas or an SF₆ gas, wherein the first fluorine-containinggas is different from the second fluorine-containing gas, and the firstfluorine-containing gas and the second fluorine-containing gas arediffer in reactivity with the silicon-containing film.
 2. The method ofclaim 1, wherein the supplying the first fluorine-containing gas and thesecond fluorine-containing gas by turns is performed in a repetitivemanner.
 3. A non-transitory computer-readable storage medium storing aprogram that operates on a computer of a controller for controlling anetching apparatus and that causes the computer to perform the etchingmethod of claim 1 by the etching apparatus.
 4. The method of claim 1,the first fluorine-containing gas further includes a NH₃ gas.
 5. Themethod of claim 2, wherein an amount of etching is gradually reduced ineach repetitive process of the supplying the first fluorine-containinggas and the second fluorine-containing gas by turns.